The present invention pertains to molded plastic parts for attachment to a supporting member. More specifically, the present invention relates to clip house mounting structures which provide improved flexural characteristics and structural strength in the corresponding part.
Injection molded plastic parts are commonly used in the automotive industry for side panels, spoilers, dashboards, armrests, wheel covers, filler panels, trim pieces, bumpers, side-sill garnishes, rocker panels and the like. Typically these parts are provided with a painted, or other decorative surface such as by means of film lamination techniques. In such film lamination techniques, a paint film laminate is co-molded over an external show face surface of the plastic part. The film laminate is typically pre-formed, inserted into a mold cavity, and a thermoplastic resin is injected under pressure into the mold cavity against the backside of the laminate. The result is a plastic part having a film laminate co-molded over a plastic substrate. Laminated paint films are detailed in U.S. Pat. No. 5,514,427, the entire disclosure of which is incorporated by reference herein. Techniques for preforming paint film laminates and insert molding film-plastic parts are disclosed in U.S. Pat. No. 5,599,608, the disclosure of which is incorporated herein by reference.
These plastic parts are typically provided with a series of integrally molded attachment means for securing the part to the given support member. Structural strength of the attachment means is dependent upon the thickness of the plastic at the intersection of the attachment means with the remainder of the part to be supported. Thick plastic sections tend to impose shrink lines and sink marks in the show face surface when the plastic solidifies. U.S. Pat. No. 6,171,543, the disclosure of which is incorporated herein by reference, provides a reinforcing rib interposed between the connection of the clip house structure and the hidden side of the corresponding plastic part. The rib provides the required strength while limiting the thickness of plastic material proximate the show face surfaces of the part. Thereby, formation of shrink lines and sink marks in the show face surfaces, due to plastic shrinkage, are minimized.
In some elongated, injection molded automobile parts such as a rocker panels and side sill garnishes, excessive sagging has been noted along the top substantially planar horizontal portions of the part that are located between adjacent clip house mounting structures. Although applicant is not bound to any theory as to the reason for such sagging, it is thought that same occurs due to shrinkage of the plastic after the molding step. Accordingly, there is a need in the art to provide improved structure for attachment of the clip house to the part so as to inhibit sagging or plastic warpage between these clip house structures along the length of the part.